Before complaining Firefox for high memory usage, check you’ve Adblock Plus extension installed says Mozilla. Using popular Adblock Plus add-on to block ads in Firefox browser and feeling it not only does block ads, but also helps pages to load quickly in the browser, you’re wrong. Mozilla’s claims that in fact Adblock Plus is greatly increasing memory used by Firefox, that’s a surprise.

Mozilla’s Nicholas Nethercote who is working on MemShrink project that aims to reduce Firefox memory consumption details the causes for this in his blog, first, by just enabling ABP there is spike in memory usage by 150 MB, he feels this could be mostly due to additional JavaScript memory usage. 

Second,"there’s an overhead of about 4 MiB per iframe, which is mostly due to ABP injecting a giant stylesheet into every iframe. Many pages have multiple iframes, so this can add up quickly"

ABP developer, Wladimir Palant responds to the first one  by saying"Concerning the general memory usage (JS objects), https://issues.adblockplus.org/ticket/145 should help here. This will allow us to use typed arrays for data storage which will be much more efficient."

And for the second, that of Stylesheet one, he says "Concerning that stylesheet – we have two projects running that might end up reducing the number of filters eventually, but other than that I don’t think we can do much about it"

Palant further explains "the purpose of that stylesheet is to hide things that cannot be blocked – a feature called element hiding. As far as Adblock Plus is concerned, only one stylesheet is created and registered globally. There is one rule for each element hiding filter meaning roughly 20 thousands right now if you are using EasyList. The fact that Firefox internally creates a separate (and not exactly small) stylesheet for each frame is something I only learned with https://bugzilla.mozilla.org/show_bug.cgi?id=988266."

Mozilla’s Nicholas concludes: it is good that add-on s blocking ads, hence you can allow it use the extra memory, but if you’re using PC with low configuration, you might have different priorities. He expresses the hope to work with ABP authors to solve this,"if you hear people complaining about Firefox’s memory usage, one of the first questions to ask is whether they have ABP installed."

So what do you say now, Adblock Plus User?